Light primer strikes with crater?

[Anthonyc]

At the range today, I noticed quite a few of my fired cartridges had these light (ish) primer strikes with craters. I’m using a howa 1500 in 6mm CM and using Starline small primer brass, Winchester small primers and Hybrid 100V, slightly higher than medium charges. The pic has what looks to be normal strikes and the right are the weird ones. Cratered primers but a light strike. The left and right rounds were of the same powder/brass/primer/bullet/etc combo. Any thoughts? I got about 10 of these weird ones out of 45 rounds. I appreciate any ideas!

 

[Anthonyc]

One more mention, I checked headspace after to see if the weird ones had less expansion but they were the same as the “normal” fired cases.

 

[ken4570tc in WY]

Looks to me to be pressure related - note how the anvil is driven back against the cup and produces a small but noticeable peak in the center of the crater.

 

[Anthonyc]

Looks to me to be pressure related - note how the anvil is driven back against the cup and produces a small but noticeable peak in the center of the crater.

good observation. I’ve had nothing but issues with this starline brass. I wonder if there’s inconsistency in the thickness of the brass, perhaps these 10 or so pieces are a bit thicker resulting in higher pressure ...

 

[ken4570tc in WY]

What primer, bullet and charge weight? Also, did you chronograph the rounds fired, if so what velocities did you see?

 

[Anthonyc]

What primer, bullet and charge weight? Also, did you chronograph the rounds fired, if so what velocities did you see?

Winchester small primers, 37.6-38.4 of Hybrid 100V in 0.2 increments - all increments had at least 1 of these weird strikes and using Hornady 108 ELD-Ms. I haven’t chronographed yet. That was the next range trip.

 

[ken4570tc in WY]

Your charge weights look modest enough that it shouldn't be pressure. What device do you use for seating your primers?

 

[Anthonyc]

Your charge weights look modest enough that it shouldn't be pressure. What device do you use for seating your primers?

Rcbs Hand primer and pockets have been uniformed with the Sinclair uniformer. I am seating 20 thou off the lands. Perhaps I should back off more?

 

[Anthonyc]

Rcbs Hand primer and pockets have been uniformed with the Sinclair uniformer. I am seating 20 thou off the lands. Perhaps I should back off more?

Just to note, I do inspect and run my finger over back of case after priming each case.. I reload for many other rifle cartridges and this issue is a first for me.

 

[ken4570tc in WY]

I'm working with Starline .243 brass and found the primer pockets were deeper than I was expecting. I also used the Sinclair carbide uniformer but had to seat the various LR primers .007 to .011 below flush to make sure every anvil was touching. I wouldn't have known except I measured the pocket depths and primer heights before seating. Is it possible that some lube has migrated in the bolt assembly and causing a hydraulic bind when the pin drops?

 

[Anthonyc]

I'm working with Starline .243 brass and found the primer pockets were deeper than I was expecting. I also used the Sinclair carbide uniformer but had to seat the various LR primers .007 to .011 below flush to make sure every anvil was touching. I wouldn't have known except I measured the pocket depths and primer heights before seating. Is it possible that some lube has migrated in the bolt assembly and causing a hydraulic bind when the pin drops?

I’ll pull it apart tomorrow and check. It’s possible. I do very, very lightly grease and then wipe the bolt surface every time I clean.